Sectional doors have long been employed in both residential structures, and commercial and industrial buildings. Sectional doors save space by retracting above, rather than into, the space they enclose. Originally, the panels of sectional doors were made of wood. However, over time, exposure to the outdoor environment causes wooden panels to rot, splinter, crack, and split. As an alternative to wooden panels, sectional doors with panels made of metal, such as steel or aluminum, have become commonplace. These metal panels have many advantages. For example, when insulation is sandwiched between two metal facers, the resulting panels have superior thermal properties as compared with wooden panels. Furthermore, metal panels are lighter than wooden panels. The savings in weight allows smaller motorized door openers to be used thus decreasing the amount of energy required to open and close the door. However, the thinner gauge metals currently being used for door panels make it desirable to use additional components for reinforcement and structural rigidity. These structural reinforcing components are attached to either the interior or exterior surfaces of the door panels, and allow the sectional doors to withstand adverse weather conditions like high winds, while, at the same time, maintaining weight savings and environmental resistance characteristics over wooden panels.
In the past, structural reinforcing components of sectional doors were fastened to the metal door panels using mechanical fasteners such as screws and rivets. Ideally, the interface between the door panels and the structural reinforcing components should be sufficiently rigid to enable the structural reinforcing components to enhance the overall strength of the door panels.
The use of thinner gauges of metal, however, prohibits a rigid interface without using a great number of mechanical fasteners. For example, the structural reinforcing components are attached to the door panels by mechanical fasteners at various spaced intervals. At these connection points, the mechanical fasteners transfer forces (i.e. high winds) from the door panels to the structural reinforcing components. However, the forces imparted to the door panels are effectively concentrated at these connection points. The concentration of force has a tendency to cause the thinner gauges of metals to warp at these connection points. Such warping can cause the door panel to eventually “tear” thereby destroying the interface between the door panels and structural reinforcing components. Nevertheless, the forces imparted to each point of connection can be decreased by increasing the number of fasteners and corresponding connection points. However, increasing the number of connection points also increases the complexity and the cost of manufacturing sectional doors. Furthermore, some metal fasteners have a tendency to deteriorate with exposure to the elements. Such deterioration can also destroy the interface between the doors panels and the structural reinforcing components.
As an alternative to mechanical fasteners, adhesives have been used to attach structural reinforcing components to door panels. Unlike attachment via mechanical fasteners, adhesives may provide a more uniform interface between the door panels and structural reinforcing components. Therefore, the forces imparted to the door panels, instead of being concentrated at the connection points of mechanical fasteners, are spread over the entire interface between the door panels and structural reinforcing components. As a result, the possibility of warping or tearing the doors panels is significantly decreased.
The use of adhesives, however, creates another set of problems. For example, quick setting adhesives such as hot melts have been used to provide a bond between door panels and structural reinforcing components. However, with quick setting adhesives, there is little structural strength imparted to the panels and there is a loss of adhesion when the doors are exposed to the elevated ambient temperatures existing in hotter climates. Consequently, high-speed assembly using quick setting adhesives has been possible, but the use of such adhesives in hotter climates has been restricted.
As an alterative to quick setting adhesives, slow setting structural adhesives have been used. These structural adhesives generally do not deteriorate in elevated temperatures, but they are slow setting, and can take up to a week to achieve their desired strength. During this curing period, the door panels cannot be handled roughly, let alone shipped and installed. Consequently, high-speed assembly using structural adhesives has been difficult. In some instances a combination of fasteners and adhesives has been employed to attach structural reinforcing components. However, the cost, labor to install and possible deterioration of fasteners remain as significant disadvantages. Therefore, existing ways of attaching structural reinforcing components to door panels, whether using mechanical fasteners, quick setting adhesives, or structural adhesives, suffer one or more disadvantages.